Byron Steelbeard

Special Equipment. Byron wears the Robes of the Archmagi giving him a base AC of 15+DEX, Advantage on saving throws against spells, and +2 to his spell save DC and spell attack roles.
Byron has equipped a Belt of Cloud Giant Strength
Byron wields a +3 shield
Byron is attuned to The Staff of the Immortal Wizard Emperor giving him access to the following spells: arcane lock, banishment, conjure elemental, dispel magic, detect magic, enlarge/reduce, fireball (7th-level version), flaming sphere, ice storm, invisibility, knock, light, lightning bolt (7th-level version),  mage hand, passwall, polymorph,  protection from evil and good, telekinesis, wall of fire, or web.
It also gives him +2 to attack roles and damage rolls, +2 to AC, +2 to spell attack rolls and spell save DC. 

Adamantine Plated Bones. Byron is immune to critical damage. 

Arcane Recovery (1/Day). When he finishes a short rest Byron recovers all of his spell slots of 5th level and lower.

Legendary Resistance (3/Day). If Byron fails a saving throw, he can choose to succeed instead.

Rejuvenation. If he has a phylactery, when Byron dies he regains a new body 1d10 days later. The new body appears within 5 ft of his phylactery. 

Spellcasting. Byron Steelbeard is a 20th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 26, +18 to hit with spell attacks). Byron has following Wizard spells prepared:
Cantrips (at will): Chill Touch, Fire Bolt, Mage Hand, Mending, Mind Sliver, Prestidigitation 
1st level (4 slots): Charm Person, Hideous Laughter, Magic Missile, Shield
2nd level (3 slots): Alter Self, Cloud of Daggers, Darkness, Tasha's Mind Whip
3rd level (3 slots): Animate Dead, Counterspell, Haste, Summon Undead
4th level (3 slots): Banishment, Fabricate, Greater Invisibility
5th level (3 slots): Cloudkill, Danse Macabre, Wall of Force
6th level (2 slots): Create Undead, Disintegrate, Soul Cage
7th level (2 slots): Finger of Death, Teleport
8th level (1 slot): Dominate Monster, Feeblemind
9th level (1 slot): Shapechange, Wish

Undead Thralls. Whenever Byron creates an undead using a necromancy spell, it has additional benefits:
 - The creature's hit point maximum is increased by 20
 - The creature adds +8 to its damage rolls.

Multiattack. Byron makes 2 attacks with a weapon and or Paralyzing Touch. 

Melee Attack. Melee Weapon Attack: +19 to hit, reach 5 ft., 1 target. Hit: 16 (1d8 + 11) bludgeoning damage + 22 (4d10) fire damage. 

Paralyzing Touch. Melee Spell Attack: +18 to hit, reach 5 ft., 1 target. Hit: 10 (3d6) cold damage. The target must succeed on a DC 26 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. 

Command Undead. An undead that Byron can see within 60 feet must make a Charisma saving throw (DC 26). If it succeeds, he can't use this feature on it again. If it fails, it becomes friendly to him and obeys his commands until he uses this feature again.

Intelligent undead are harder to control in this way. If the target has an Intelligence of 8 or higher, it has advantage on the saving throw. If it fails the saving throw and has an Intelligence of 12 or higher, it can repeat the saving throw at the end of every hour until it succeeds and breaks free.

Spell Absorption. Byron can use his reaction when another creature casts a spell that targets only him. If he does, the staff absorbs the magic of the spell, canceling its effect and gaining a number of charges equal to the absorbed spell's level. However, if doing so brings the staff's total number of charges above 50, the staff fails to absorb the spell.

Byron can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Byron regains spent legendary actions at the start of his turn.

Staff of the Immortal Wizard Emperor (1). Byron may cast a spell from the list of spells provided by his staff.

Melee attack (1). Byron may make one melee attack with either his staff or Paralyzing Touch to a creature within reach. 

Command (2). Byron may command one of his subjects that can hear him, allowing it to  immediately take an action. 

Disrupt Life (3). Each non-undead creature within 20 feet of Byron must make a DC 26 Constitution saving throw against this magic, taking 21 (6d6) necrotic damage on a failed save, or half as much damage on a successful one.